I have heard of people cross contaminating kefir with vili by accident. The result is "kefilli" and not suposed to taste too great. I would be very interested in the results of fil mjolk with kefir. Unfortunately, I never thought of mixing the two when I still hadboth in use, and always kept them on separate counters.
I would steer away from honey in your experiments, as it may kill the bacteria in yogurt and in kefir. Mix it in afterwards, but not during incubation/fermentation.
BTW: I have been making thermophilic yogurt for over 20 years... Got my first yogurt maker when I was still in highschool. Rule number one has always been to not let metal touch anything.
Looking forward to hearing about your experiments!